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Infant-Directed Speech: An Optimal Signal for Early Speech Processing
Poster C99 in Poster Session C, Wednesday, October 25, 10:15 am - 12:00 pm CEST, Espace Vieux-Port
Marina Kalashnikova1, Laura Fernandez-Merino2, Nicola Molinaro3; 1Basque Center on Cognition, Brain and Language, 2Ikerbasque, Basque Foundation for Science, 3University of the Basque Country
Adults adjust their speech during face-to-face interactions with infants. The resulting speech register, known as infant-directed speech (IDS), is proposed to promote infants’ early language development. Specifically, the exaggerated prosodic patterns and phonetic expansion characteristic of IDS are proposed to facilitate more efficient encoding and processing of the speech signal. This proposal is supported by recent evidence for more successful cortical tracking of IDS compared to adult-directed speech (ADS) in young infants. Cortical tracking refers to the synchronisation between the oscillatory neural activity and the temporal modulations in the amplitude envelope of the speech signal. The frequency bands of neural oscillations specifically relevant for speech processing are delta (<3 Hz) corresponding to phrase- and word-level prosodic rates in speech, theta (~5 Hz) corresponding to the syllabic rate, and gamma (~20 Hz) corresponding to the phonetic rate. Specifically, IDS is proposed to enhance cortical tracking of low frequency information (delta and theta), thus facilitating both infants’ recognition of the phrasal- and word-level prosodic patterns of their native language, and later reliance on these patterns for extracting words from continuous speech. While infants’ cortical tracking is more efficient for IDS than ADS, previous studies have not investigated how this benefit relates to infants’ developing linguistic abilities. For this purpose, this short-term longitudinal study assessed (1) cortical tracking of IDS vs. ADS at 4 and 9 months, before and after infants begin to successfully segment words from continuous speech, and (2) the relation between the IDS benefit on cortical tracking of speech and infants’ individual lexical processing abilities at 9 months of age. Thirty-two infants acquiring Basque completed two tasks: a cortical tracking task (at 4 and 9 months) and a lexical processing task (at 9 months). In the former, infants heard audio recordings of naturally-produced IDS and ADS while their continuous EEG was recorded. In the latter, infants watched images of familiar objects on a screen (e.g., apple and ball) while one of the objects was named (e.g., “where is the ball?), and their eye movements were recorded using eye-tracking. Data collection is complete, and analyses are currently in progress. We will calculate coherence between the neural oscillatory activity and the speech envelope in delta and theta. These frequency ranges will be defined as the rates at which stressed and unstressed syllables occur in the IDS and ADS stimuli. We predict a stronger IDS benefit (Coherence IDS > ADS in delta and theta bands) at 9 compared to 4 months, which will reflect the developmental transition to encoding prosodic patterns in the speech signal for efficient segmentation of continuous speech. Additionally, we predict that individual indices of IDS cortical tracking at 9 months will relate to infants’ familiar word recognition efficiency. These findings would demonstrate that early speech processing and the emerging ability to extract meaningful linguistic information from continuous speech in the first year of life is supported by early neural maturation, infants’ growing linguistic ability, and critically, the quality of speech that infants hear in early interactions with their caregivers.
Topic Areas: Language Production, Signed Language and Gesture